By taking the place of incandescent lamp and fluorescent lamp, a light emitting device of an optical semiconductor (light emitting diode, LED) has come into wide use. Though there are various types in the white light LED device, the main stream of the current white light LED device is a light emitting system in which white light is emitted as a mixed color of blue and yellow by using a blue light emitting element and dispersing a phosphor which converts blue color to yellow color in an encapsulating resin.
In recent years, development of light emitting elements is proceeding at a fast pace, and by taking the place of the conventional low luminance white color package mainly including a shell type, a high luminance white color LED package which can also be used in the back light of general lighting fixture and liquid crystal television is becoming the main current. Thus, since the epoxy resin conventionally used as an encapsulating resin causes a problem in that its transparency is lowered due to deterioration by light and heat, a resin having less deterioration, such as silicone, has been used. On the other hand, the silicone resin shows good durability, but in general, it is necessary to mold a package from liquid state so that its poor workability at the time of encapsulation is causing a low throughput and further a high cost.
Based on these reasons, an encapsulation method which uses an encapsulating sheet has been proposed instead of the encapsulation method that uses a liquid matter, so that a sharp improvement of workability has been made. In addition, since the light-extraction efficiency can be improved by arranging a wavelength conversion layer at a place distant from the light emitting element, namely at the outermost side of the package, the method for preparing a package using an encapsulation sheet is drawing attention also from the viewpoint that a uniform wavelength conversion layer can be easily formed in the outermost layer.
Preparation of a package using an encapsulating sheet is generally carried out by putting an encapsulating sheet and a concave mold on a light emitting element in this order and carrying out compression molding. In this case, a uniform wavelength conversion layer is formed on the outermost side of the package in each of the upper side and side surface (lateral part) of the light transmitting element. Accordingly, the light-extraction efficiency is high so that it becomes possible to obtain a light device.
However, when the orientation condition of emitted light, namely color distribution of light at each angle of radiated light, is examined in detail, there is a tendency in that the light radiated toward the wide-angle direction becomes dense in color, in comparison with the light radiated toward the front direction. This is because the light radiated toward the wide-angle direction passes through a long distance of the wavelength conversion layer in comparison with the front direction. Accordingly, in the case of a package having a relatively low height which is prepared using an encapsulating sheet, difference in chromaticity at respective angles, namely angle-dependency of chromaticity, is so large that difference in the chromaticity of light becomes a problem depending on the looking direction when used in illumination and the like.
In order to improve this problem, there has been proposed a dome type package in which height of the package was heightened and also the lateral part wavelength conversion layer was arranged in such a manner that it becomes perpendicular to the light emitting element (cf. Patent Document 1).
Patent Document 1: JP-A-2008-159705